Cadmium Fractions in Two Calcareous Soils Affected by Incubation Time, Zinc and Moisture Regime

This study has been performed to determine the impact of zinc (Zn) on cadmium (Cd) fractions in two types of calcareous soils of the Fars province in Iran at the waterlogged condition. High-reduced conditions in soil reduce Cd solubility because of the development of Cd Sulfide. Cadmium and Zn have similar physical-chemical properties; they are maintained in soil's exchangeable sites as a divalent ion. Since such few studies have been conducted in calcareous soils of Iran, we examined the effect of Zn on Cd fractions due to their similar characteristics. Treatments were three levels of Cd (0, 30 and 60 mg kg(-1) of soil as CdSO4.8H(2)O), three levels of Zn (0, 5 and 10 mg kg(-1) of soil as ZnSO4 .7 H2O), three levels of incubation times (2, 4 and 8 weeks), and two types of soils (clay and sandy clay loam). The randomized completed block design (RCBD) was used for this experiment. After 2, 4, and 8 weeks of treatments, the sequential extraction technique was used to determine the Cd concentration in (WsEx), (Fe-MnOx), (Car), (OM) and (Res.) fractions. The data indicated that based on the soil texture 64% to 70% of the Cd was extracted in the WsEx and Fe-MnOx fractions. The waterlogged condition decreased the Cd concentration in the WsEx fraction and increased the Fe-MnOx, Car and OM fractions. Cd concentration in Res. fraction was higher in the clay soil while WsEx, Car and OM fractions were higher in the sandy clay loam soil. Adding Zn as zinc sulfate reduced the concentration of Cd in Fe-MnOx, Car and OM fractions but had no significant effect on the WsEx and Res. fractions. It can be concluded that the change in the Cd concentration in its chemical fractions caused by Zn addition might be from the competitive transport and adsorption interaction between these two ions. The presence of Zn reduces the concentration of Cd in those forms that are easily released into the soil solution from where they can be absorbed by plants.